Brushholder



Feb. 24; 1959 .1; w; ERICKSON BRUSHHOLDER 2 Sheets-Sheet 1 Filed June 19, 1957 Feb. 24, 1959 J. w. ERICKSON BRUSHHOLDER 2 Sheets-Sheet 2 Filed June 19, 1957 Fig. 3.

United States Patent" M 2,815,251 BRUSHHOLDER JolmW; Erickson, Ea'st'Anrora', N.'Y., assignor toWestmghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application June19, 1957, Serial No. 666,698 2 Claims; (Cl; 310-246)" The present invention relates to brushholders for dynamoelectric machines and, more particularly, to a brushholder capable of providing a substantially constant brush pressure throughout the life of thebrush.

In commutator type dynamoelectric machines maintenance of a constant brush pressure on the brush as it rides on the commutator surface is necessary for satisfactory commutation and machine performance. A constant brush pressure throughout the life of the brush tends to maintain constant contact drop between the brush and the commutator surface, and maintains proper riding of the brush on the commutator. In manyconventional designs, the pressure to which the brush is subjected varies as the br'ush'wears throughout its life, thereby failing to provide a substantially constant contact drop for. satisfactory commutation. Occasionally, a different constant .pressure'is desired on the brush. On this occasion, changing the brush pressure usually requires changingbiasing means such'as using a different spring. This necessitates a variety of springs to be kept on hand for operation of the machine. When brushes are to be replaced, a quick and positive method of disengaging the brushpressure means is also desirable;

The principal object of my invention is to provide a brushholder capable of exertinga substantially constant pressure on the brush during the entire length of the brush. life.

Another object is. to .furnish'means whereby brush pressure can be changed at any time without replacing the original spring.

Another object is to provide for positive disengagement of the pressure means from the brushwhen desired, allowing easy changing and inspection of the brush.

Other objects and advantagesof the invention .will be apparent from" the following detailed description; taken in connection" with theaccompanying drawings, in which:.

Figure l is a schematic diagram. illustrating the manner ll1.WhlCh my invention obtains the desired" results;

Fig. 2 is a graphical representation of the variation of the forces involved in the diagrammatic system of Fig. 3 is a side view of a brushholder embodying my invention;

Fig. 4 is a top view of the brushholder shown in Fig. 3; and

Fig. 5 is an end view of the left-hand side of the brushholder illustrated in Fig. 3.

The principles of my invention are diagrammatically illustrated in Fig. 1, which shows a lever arm DE pivotally mounted at a fixed point E, with a tension spring G attached to the lever arm DE at point D. The opposite end of spring G is pivotally mounted at a fixed point P. The pivot points E and F are located at predetermined spaced points.

2 ,875,357 Patented Feb. 24, 1959 arm DE tending to rotate the lever arm DE about'its pivot E. The lever arm DE has two extreme positions BE and AE, as shown. At the one extreme BE, the tension spring G is at maximum elongation, but since the pivot point E of the lever'arm DE is located on the line of action of the spring G, the moment arm tending to rotate the lever arm DE is of zero magnitude. At the other extreme position AE, the tension spring G is at minimum elongation and applies no force to the lever arm DE, so that in this position, the lever arm DE is again subjected to no turning moment. As can be seen, between these two extreme positions, there is a turning moment applied to the lever arm DE by means of the tension spring G which will vary with the displacement angle a.

Fig. 2 is a graphical representation of the turning moment to which the lever arm DE is subjected for values of angular displacement or between the two ex tremes BE and AE. It will be noted that within an intermediate range CE to DE, the change in angular displacement on has very little elfect upon the turning moment acting upon lever arm DE. In this range of travel, the change in the effective moment arm and the change in the force applied by the tension spring G are substantially equal and opposite. The result is that within this range of angular displacementa the lever arm DE is subjected to a substantially constant turning moment. In applying this system to a brushholder, positions CE and DE' are chosen to correspond to the normal range of travel corresponding to the brush life.

Fig. 3, which is an illustrative embodiment of my invention, shows a brushholder utilizing the principles described'in connection-with Figs. 1 and 2. The brushholder is comprised of a brushholder body 6 with a brush box 3, herein shown integral therewith, for receiving a brush. Lever arm 1 with a pressure finger 2, preferably integral with the lever arm 1, is pivotally mounted holder body 6 on a pivot 10. The opposite end of the" tension spring 5 is attached to the lever arm 1 through suitable means such as a clip 7. Pressure finger 2 engages a brush within the brush box 3 to hold the brush against the peripheral surface of a commutator indicated at 17. The brushholder body 6 and the brush box 3 may be formed with a recess 14 adaptable to suitable brush rigging for holding and positioning the brushholder in place, or the brushholder may besupported in position in any other suitable manner.

ComparingFig. 3 with Figs. 1 and 2, it can be seen thatthe lever arm pivot 4 and the tension spring pivot 10 are located in a fixed relationship to each other. The tension spring 5 is attached to the lever arm 1 for apply-' ing a force on the lever arm 1 about its pivot 4. The lever arm pivot 4-and the tension spring pivot 10 are positioned'so that as the brush wears down in length, the normal range of angular'movement of the leverarm 1 willcorrespond to the range of movement between CE and DE, as illustrated in Fig. 1. It is in this range that a substantially constant turning moment is applied to the lever arm 1, as illustrated in Fig. 2. The lever arm 1 acting upon the pressure finger 2 shown integral therewith transmits a component of the substantially constant force to the brush within the brush box 3, thereby applying a substantially constant brush pressure throughout the normal life of the brush.

The spring clip 7, used to attach the tension spring 5 to the lever arm 1, has a plurality of openings 9 for selectively engaging a lug 8 integral with lever arm 1 which protrudes through an opening 9. A projection 15 integral with the spring clip 7 may have a hole therethrough, or other suitable means, for attaching the ten-' in place on its pivot by clamping over the tension spring pivot 10 after the tension spring 5 has been mounted. A terminal screw 12 and terminal washer 13 may be provided 'for connecting to a brush pigtail.

Fig. 3 shows the brushholder with its lever arm 1 and integral pressure finger Zin a position corresponding1to anew brush. From this figure, it can be seen that the tension spring 5 applies force upon the pressure finger 2 by means of the lever-arm 1. Lever arm pivot 4 and tension spring pivot 10 are located on the brushholder body 6 in such relative positions that the lever arm 1 rotates through an angular displacement a corresponding to CE to DB, for a normal brush life, such that the perpendicular distance between the lever arm pivot 4 and the line of action of the tension spring 5 will change substantially equal and opposite to the force applied to the lever arm 1 by the tension spring 5. Thus, the product of the eiiective lever arm and the tension spring 5 force remains substantially constant within this preselected angular displacement corresponding to the expected brush life, and the brush pressure remains substantially constant.

Easy inspection or brush changing is.accomplished byfli'cking the pressure finger 2 up away from the brush box 3. In so doing, the lever arm 1 will assume a posi-' tion equivalent to BE in Fig, 1. In such a position the tension spring 5 cannot tend to rotate the lever arm 1 since the efiective'moment arm is zero. If the lever arm 1 is rotated farther than BE, a positive pressure tending to rotate the lever arm 1 farther away from the. brush will effectively lock the lever arm 1 and brush finger 2 out of position. The lever armyl is thus held out of the way to permit the brush to be changed easily.

A particular embodiment of my invention has been described, but other variations can be used; for example, when double or split brushes are desired to be used in the brush box 3, it is a simple matter to utilize a somewhat larger brush box with another lever arm having a longer pressure finger mounted on the opposite side of the brushholder body 6 for engaging the other brush within the brush box '3. This lever arm would be actuated by a duplicate tension spring 5 mounted on the opposite side of the same brushholder. In this arrangement, both brushes will be subjected to a constant pressure in the same manner as described previously. When this is done, a second spring'clip 7, being a mirror image of the one described and placed on the opposite side of the brush body 6, may be employed as the means for connecting the second lever arm to the second identical tension spring 5. The U-shaped retaining clip 11 can be made to retain both springs 5 on their common tension spring pivot 10 by clamping over the tension spring pivot 10 after both tension springs 5 have been mounted.

It will now be apparent that my invention provides a v r relatively simple structure with a unique spring and lever arrangement for furnishing a constant pressure on a brush throughout its entire life. If it becomes necessary to change pressure on the brTlsh, the same tension spring 5 is utilized for any desired number of different pressures by selectively biasing the tension spring 5 through the selecting means supplied byithe .clip 7. If inspection or replacement of a brush is desired, the lever arm 1 will lock out of position with a flick of the finger, clearing the-brush box and allowing brush inspection or changing with one hand.

While certain specific embodiments of the invention have been shown and described for the purpose of illustration, it is to be understood that other embodiments and modifications are possible and are within the scope of this invention.

I claim as my invention:

,l. A brushholder assembly comprising means for holding a brush in position to engage a commutator, av lever arm pivotally supported in position to engage the brush to apply pressure'thereto, a tension spring having one end pivotally supported at a fixed point and the other end attached to the lever arm to apply a turning moment thereto, the pivot points of the lever arm and spring being spaced apart and positioned so that said turning moment is substantially constant throughout a predetermined range of movement of the lever arm, a lug integral with said lever arm, and an engaging member carried on said lever arm, said member having a plurality of openings for selectively receiving said lug, means on said member for attaching one endof the tension spring,

and means for manually engaging and disengaging said member from the lug.

2. A brushholder assembly comprising means for holding a brush in position to engage a commutator, a lever arm pivotally supported in position to engage the brush to apply pressure thereto, a tension spring having one end pivotally supported at a fixed point and the other end attached to the lever arm to apply a turning moment thereto, the pivot points of the lever arm and spring being spaced apart and positioned so that said turning moment is substantially constant throughout a predetermined range of movement of the lever arm, said lever arm being movable away from the brush to an extreme position in which the turning moment on the lever arm is zero, a lug integral with said lever arm, and an engaging member carried on said lever arm, said member having a plurality of openings forselectively receiving said lug, means onr'said member for attaching one end of the tension spring, and means for manually engaging and disengaging said member from the lug.

References Cited in the file of this patent I 

